std: Standardize (input, output) param orderings

This functions swaps the order of arguments to a few functions that previously
took (output, input) parameters, but now take (input, output) parameters (in
that order).

The affected functions are:

* ptr::copy
* ptr::copy_nonoverlapping
* slice::bytes::copy_memory
* intrinsics::copy
* intrinsics::copy_nonoverlapping

Closes #22890
[breaking-change]

src/liballoc/heap.rs

@@ -301,7 +301,7 @@ mod imp {
             libc::realloc(ptr as *mut libc::c_void, size as libc::size_t) as *mut u8
         } else {
             let new_ptr = allocate(size, align);
-            ptr::copy(new_ptr, ptr, cmp::min(size, old_size));
+            ptr::copy(ptr, new_ptr, cmp::min(size, old_size));
             deallocate(ptr, old_size, align);
             new_ptr
         }